Export TGA or BMP textures for WebGL
There is an addon to batch convert image files with blender.

After installing the addon, the usage is simple:


Tell the addon where the folder of images is (must contain only the images to convert)
Give it a output folder
Set the render settings correctly (you will want PNG)
Click the Batch convert button.




To keep the original file sizes, check the Keep Original Resolution check box in the Batch Converter settings in the tool shelf.